When certain resin based compositions are exposed to solvents the resins may be adversely affected by the degradative effects of the solvent. In addition, there is a need for coating compositions that are capable of functioning as a so called primer for resin based, non-metallic alloy compositions. For example, automotive assemblies are made from various resin systems known as non-metallic alloys that require individually specialized painting systems. This procedure does not permit prior assembly of parts followed by a one-step painting operation.
Examples of this problem are the use of a polyurethane reaction injected molding composition for an automotive fender and the use of sheet molding compound for the front hoods. These body parts cannot be painted at one time because of overspray.
Other resin compositions such as the polycarbonates have exceptional properties that permit them to be used for applications, such as automobile bumpers, where they are likely to be exposed to aggressive hydrocarbon solvents. It is well known that aggressive solvents such as premium unleaded gasoline can adversely affect or completely destroy these resins.
The applicant has discovered a composition which comprises an aqueous colloidal dispersion of an aliphatic urethane, an anionic surfactant and a carbon containing pigment that is thermally curable to a coating which adheres tenaciously to a wide variety of substrates. This coating can function as a primer for a subsequent painting step or will function as a solvent resistant protective coating.
The use of this type of a composition which relies on surface adhesion is vastly different from currently used produces that rely on solvent "etching" to slightly degrade the surface of resinous materials to form bonding sites for the any coating that is subsequently applied.